1. Field of the Invention
The present invention relates to controls for prime movers or engines, and particularly to electronic controls for engines employed in vehicles or other applications where power and speed are to be managed in accordance with one or more factors such as operator demand, emission requirements, temperature, load, and/or other conditions.
2. Description of the Prior Art
One type of prior art control for controlling fuel flow, speed, torque and emissions of a diesel engine employs a fuel pump having a cam shaft driven by the engine for operating a plurality of injection pumps feeding fuel to the corresponding cylinders of the engine. The accelerator pedal is connected by linkage to a rack in the fuel pump which controls valves or port members associated with the injection pumps for controlling the quantity of fuel delivered by the injection pumps to the engine cylinders. A mechanical governor with a flyweight is driven by the injection pump cam shaft to control the positioning of a governor lever with a specially contoured limiting cam or cams in accordance with engine speed or rpm to limit the maximum rack position and thus the maximum fuel delivered to the engine; these governor cams are designed to produce selected maximum torque, power and emission characteristics. Additionally, the governor, upon engine speed or rpm exceeding a maximum safe speed, will move the lever to retract the rack to terminate or greatly reduce fuel flow to prevent damage to the engine. Fuel pumps with different governor cams must be manufactured and stockpiled in order to produce a desired variety of engines with different torque and power characteristics. Variations in dimensions and characteristics of cams, governors and fuel pumps under normal manufacturing techniques result in the requirement of extensive adjustments in the positioning of the levers and cams during final engine testing at several engine speeds in order to produce the desired engine characteristics and compensate for engine variations in manufacturing; adjustment of lever angle of position, for example, in a later step may necessitate repositioning of a cam or cams set in an earlier step. Additionally, these adjustments must also be done on governor replacements made in the field, i.e. when a new or reconditioned governor is installed on a pump.
Concern about pollution of the environment has resulted in requirements for engines to limit emissions of certain substances including incompletely burnt fuel which can be produced by sudden depression of an accelerator pedal and a large sudden increase in fuel delivery exceeding the fuel to air ratio necessary for complete combustion. In the above-mentioned type of diesel engine employing a rack controlling fuel delivery, one prior art emission control utilizes dampening facilities to prevent rapid advance of the rack. This necessarily reduces the maximum acceleration of the engine. Manufacturing tolerances needed to insure compliance with emission requirements result in a further reduction in maximum acceleration.
Tampering with the governor or its settings and/or emission controls in order to increase the maximum power speed and/or acceleration characteristics of the engine continues to be a problem in spite of sealing of the governor and providing warnings of dire consequences of tampering. Truck fleet companies select engine power characteristics designed to prevent or limit operation of the trucks at excessive speeds. Tampering with the governor and/or its settings and/or alteration or removal of pollution controls enables operation at higher speeds and acceleration to reach destinations sooner, but resulting in possible engine damage, more fuel consumption, violation of speed laws, and greater likelihood of accidents causing severe injury and death.
Operation of engines at higher altitudes requires lesser quantities of fuel to avoid exceeding the desired fuel to air ratio. The prior art includes devices for sensing an excessive exhaust temperature, which indicates an excessive fuel to air ratio, to operate devices mechanically limiting the maximum position and/or forcing retraction of a fuel pump rack to a position insuring a reduced fuel to air ratio.
Cruise controls, i.e. devices which will automatically maintain a set road speed to relieve the operator of the necessity to maintain a steady speed by means of the accelerator pedal, are available in the prior art. Such devices for the above-mentioned type of diesel engine are generally relatively expensive and require installation of additional equipment, e.g. devices to automatically operate the linkage from the accelerator pedal to the fuel pump in response to sensed vehicle road speed.
Emission control and fuel economy requirements, principally in gasoline operated automobiles, have resulted in the extensive development of electronic controls for engines, including computerized controls. Typically these systems regulate the air to fuel ratio to achieve optimum emission control and/or economy. Generally the computerized systems employ memory tables, and measured values such as engine speed and manifold pressure or throttle position, which correspond to air intake, to select a value corresponding to fuel quantity from a table. These looked-up values are typically used to determine the length of injection pulses applied to electrically operated fuel injection valves associated with corresponding cylinders of an engine. Other detected values, such as engine water or oil temperature, catalytic convertor temperature, altitude, air temperature, acceleration, deceleration, cranking voltage, and exhaust gas composition, have been suggested for use in modifying the values read from the tables or to define an additional table matrix or dimension. Interpolation between stored values has been employed in order to permit reduction in the size of tables. Also the prior art often selects spark ignition timing based upon stored table values and/or calculations made from various parameters. These prior art electronic control systems generally may be characterized as having one or more deficiencies such as being unstable or subject to periodic speed variation or hunting under certain speed, demand or load conditions; inability to reliably or promptly respond to varying demand or load conditions; requiring extensive memories to store multidimensional tables; requiring extensive data generation efforts; and/or other deficiencies.
Fuel controls for engines can generally be categorized as either "min-max" or "all-speed" systems. In min-max systems, such as in the above-mentioned prior art mechanical governor control system, the accelerator pedal controls the quantity of fuel delivery, or fuel pump rack position, between minimum (idle) and maximum levels which are determined by the governor in response to engine speed. In all-speed systems the accelerator pedal position corresponds to an engine speed and fuel delivery is varied to achieve that engine speed. For most vehicles such as automobile or truck applications, the min-max systems are preferred.
Prior art attempts to implement electronic or computerized controls for fuel controlled engines, such as diesel engines, and which provide acceptable vehicle driveability throughout the necessary entire wide range of drive and traffic requirements and within the constraints imposed by the engine design and the government emission requirements have generally been unsatisfactory. These prior art control systems generally have been subject to one or more deficiencies such as requiring an impractical large amount of expensive electronic equipment often too large to readily fit in available space within the truck, not being able to provide acceptable speed control throughout all of the many transient operating modes common to the operation of a truck, producing periodic speed variation (hunting) or surging in speed particularly at low speeds, resulting in engine stalling due to speed undershoot at low speeds, resulting in engine damage due to overspeeding such as that caused by overshoot, being undesired all-speed systems, being unsuitable for high pressure injection systems, etc.
Also, the prior art electronic or computerized controls wherein an engine is controlled by movement of a control member, for example the movement of a fuel control rack in a fuel pump, generally require sensing facilities for determining the positions of the control members to provide feedback to control movement. Where accurate positioning is required, such as is needed to control maximum power or torque in a diesel engine, the feedback systems generally must be relatively expensive high precision systems and/or require extensive calibration procedures during engine testing.
Fuel economy in prior art fuel control systems has been maximized by electrical, pneumatic and/or mechanical controls on the fuel pump governor operated by switches sensing gear shift position to limit fuel flow in one or more gear positions. Such prior art fuel maximizing systems have been relatively expensive as well as being susceptible to disablement and unreliability.